U are gonna get people answering here that clean their gun after every range trip - to people who only clean the gun 1x a year. So, U will get all types of answers. There is a thread on that topic someplace around here.
EVERYTIME I go shoot, I clean the gun afterwards. Also, about 1x a month, I remove the slide from the frame, and I use a toothbrush to place new oil on the rails of the frame. Oil tends to evaporate over time. While there is still some lubricity that would remain in that area, I still like to do this about 1x a month.
Also, unless I did it w/i a week or two, I also do this real quick right before a trip to the range - so I know I won't have any issues. This takes less than 1 min, though.
If you sweat on a gun - like when you are carrying it - then its probably a good idea to get some oil on a patch, rub down all the metal parts with it, and then get an old range and wipe the oil off.